Containers for hazardous powdered materials have, for a number of years, been made from thermoplastic compositions. Thermoplastic containers have the advantages that they can be made relatively inexpensively by injection molding, the construction materials are not subject to serious attack by highly corrosive contents such as sodium hypochlorite, and they can be designed to have integral closure mechanisms and the like more readily than when using metal or glass.
Such containers have very frequently been designed in the traditional cylindrical shape, however, which is very wasteful of space during shipment and storage. Those containers which are designed with a square, instead of circular, shape tend not to have a lid or closure which provides access to the entire area of the top of the container. Typically, they will have a square top which cannot be removed from the container, having a much smaller circular or other opening or spout built into it. The user can never be sure what he or she has to do to completely empty the container, since he or she cannot see into it, and the opening is seldom at a corner of the square so one can pour the contents out from one orientation.
In the past, it may have been considered expedient to design an opening smaller in area than the top of a square container so that the junction of the top and the sides of the container could be made of one piece or permanently joined, to minimize problems with impact tests such as the United Nations shipping requirements. But if that is so, it is based on an assumption that a seal around the junction of the top and the sides is too difficult to accomplish when using a removable closure.